The rapid increase in carbon dioxide emissions from industrial sources has been considered one of the main causes for the Earth's changing climate. The reduction of carbon dioxide emissions can be achieved by improving energy efficiency, implementing renewable carbon-free energy sources, and developing carbon capture, utilization, and storage (CCUS) technologies. Worldwide energy use will continue increasing; and thus, CCUS could provide an immediate solution to the global carbon imbalance while renewable energy technologies develop. By sequestering carbon dioxide, the atmospheric carbon dioxide concentration can be stabilized or reduced. Most focus in the CCUS field has been placed on amine-based carbon dioxide capture combined with geological storage. While these technologies have already been demonstrated in large scales, amine-based carbon dioxide capture process and the geological storage of carbon dioxide still face challenges such as high parasitic energy consumption during solvent regeneration and the permanence and accountability issues for long term carbon dioxide storage. Furthermore, these schemes would not allow direct integration of carbon capture and storage with high temperature energy conversion systems.
A few high temperature carbon capture schemes exist that utilize a metal oxide as carbon capture medium such as Zero Emission Coal Alliance (ZECA) process and calcium looping technologies. Numerous studies have shown that Ca-based sorbents, often in the form of Ca(OH)2 or CaO derived from CaCO3, provide substantial carbonation conversion and kinetics. Ca-based sorbents are attractive because they can be prepared using inexpensive resources such as limestone. However, since they are derived from carbonate mineral, Ca-based sorbents cannot be used as direct carbon storage. The spent sorbents need to be regenerated, requiring a significant cost and energy penalty, especially when accounting for sorbent degradation.
A more permanent way of preventing carbon dioxide from entering the atmosphere is a chemical conversion of carbon dioxide to a thermodynamically lower state. Carbon dioxide is the anhydrous form of carbonic acid and, therefore, can be used to displace weaker acids such as silicic acid. The formation of carbonates from silicates, which thermodynamically bind carbon dioxide, is a well-known process called mineral weathering. In many instances these carbonates dissolve in water, but some, such as magnesium or calcium carbonates, are remarkably stable as solids. Some of the geologically sequestered carbon dioxide will undergo mineral weathering with surroundings. However, the reaction between mineral and carbon dioxide is very slow in nature, and thus, the portion of carbon storage by mineralization is very limited in the geological sequestration. Mineral carbonation can also be performed using industrial wastes such as steel slags and fly ash. In particular, the use of stainless steel slags, which are considered to be hazardous wastes, results in carbon capture and storage with inherent treatment of hazardous wastes.
The main challenge for carbon mineral sequestration has been the slow dissolution kinetics of minerals. Most of the prior studies on carbon mineral sequestration focused on the pretreatment of the minerals, including heat treatment of serpentine and wet-attrition grinding of Mg-bearing minerals. These methods, however, are highly energy intensive and, since the current energy sources are generally fossil-based, the net amounts of carbon contained by those pretreatment schemes have been found to be significantly less than the amount of carbon dioxide reacted.